1. Field of the Invention
The present invention relates to a photosensitive resin composition for a black matrix. More specifically, it relates to a photosensitive resin composition, which can form a film having no pinhole on the surface after low pressure drying, no line or cloud defect on the film, satisfied inner uniformity and after pre-bake and high photosensitivity after pre-bake; and the black matrix having good heat resistance after post-bake, especially no poor coating on substrates of LCD by the slit coating.
2. Description of Related Art
Color filters of LCD are always desired to exhibit higher resolution and better qualities. In order to promote their contrast and related properties, light shielding films are generally formed between stripes and dots of the color filters. Generally, black matrix has been provided as light shielding films between red, green and blue pixels. Thus high quality of the contrast and hue of LCD can be obtained by shielding light to escape from gaps between the pixels.
The conventional black matrix is formed of chromium by vaporization deposition process. However, such process is complicated and the material is expensive. A solution for these problems is to apply photosensitive resin compositions to the black matrix through photolithographic processes. Japanese Patent Publication No. 08-278629 and 2003-29397 disclosed a fluorene-based alkali-soluble resin as the binder of the photosensitive resin composition, which was coated on the substrate to form a black matrix by employing the photolithographic processes. According to these disclosures, the photosensitive resin composition was first coated on the surface of a glass substrate by spin coating and was pre-baked to remove the solvent to form a pre-baked film. Thereafter, the film is exposed to UV light through a photo mask and cleaned or developed with weak alkaline solution to dissolve and remove the un-exposed portions of the film. The desired pattern of the black matrix is obtained after post-bake of the film.
In order to reduce costs for manufacturing LCD, technologies applied to large-sized substrates are continuously developed. The evolution of the sizes of the substrates for manufacturing LCD includes 320 mm×400 mm (first generation), 370 mm×470 mm (second generation), 550 mm×650 mm (third generation), and 680 mm×880 mm-730 mm×920 mm (fourth generation). In the future, as the fifth or further generation, the substrate having at least one side of longer than 1000 mm will be applied, such as, 960 mm×1100 mm, 1100 mm×1250 mm, 1100 mm×1300 mm, 1500 mm×1800 mm and 1800 mm×2000 mm, etc. The productivity can be higher when compared with that of the former generations.
For a substrate having a size of 550 mm×650 mm or lesser, the photosensitive resin composition is primarily coated thereon by the spin coating process. Though such process can easily control thickness of the films, it wastes more than 90% of the photosensitive resin composition as being spined away from the substrate. Moreover, edge beads of the photosensitive resin composition is usually formed on the peripheral regions of the substrate, which is removed with additional cleaning equipments and removing agent. So, the spin coating process costs much and is complicated in operation.
For the substrate of 730 mm×920 mm, the slit-spin coating process is applied to save the quantity of the photosensitive resin composition. In such process, the photosensitive resin composition is first coated on the substrate by slit coating, and then the substrate is spined so that the photosensitive resin material can be uniformly spread thereon. Accordingly, utilization ratio of the photosensitive resin composition can be promoted from less than 10% to about 20%. However, the problem of edge beads still exists.
As for the substrate having at least one side of longer than 1000 mm, only the slit coating process (that is, the spinless coating process) is applied, so that the photosensitive resin material can be more efficiently utilized. Related technologies are referred to “Display (Japanese Journal), November 2002, page 36, Technology and Apparatus for Manufacturing Large-Sized Substrates of Color Filters of the Fifth Generation with the Slit Coating Process” and “Electric Material (Japanese Journal), June 2002, page 107, Manufacturing of Substrates for Planar Displays with the Slit Coating Process”. Using the slit coating process without the spinning step, utilization ratio of the photosensitive resin material is approximately 100% and the problem of edge beads no longer exists. Therefore the cost for materials, equipments, removing agent and the complexity of the coating process can be greatly lowered.
However, when the photosensitive resin composition comprising a fluorene-based alkali-soluble resin is used for the black matrix by the slit coating process, it usually causes some problems, such as pinholes on the surface of the film after low pressure drying, line and cloud defects on its surface and unsatisfactory inner uniformity of the thickness of the film after pre-bake, especially no poor coating on substrates of LCD by the slit coating. Apparently, these problems have adverse effects to the high quality needs of the later large-sized LCD displays, such LCD-TV and LCD monitors.